Here we report the room temperature synthesis of stable CuNi bimetallic alloy particles under aqueous conditions using cetyltrimethylammonium bromide surfactant and hydrazine hydrate as a reducing agent. The bimetallic particles are formed in situ by the reduction of Ni2+ ions to Ni0 by hydrazine. No additional base is added to maintain the pH of the aqueous solution during the synthesis. The reduction process is favoured by Cu nuclei which formed initially. Metallic Cu nuclei assist the growth of CuNi alloy particles of all compositions with nickel-rich kernel phases. The oxidation and hydrogen uptake behaviour of the CuNi particles are found to differ significantly due to the size and intrinsic variations in composition. CuNi particles are also embedded in SBA-15 matrix by similar co-reduction method. The catalytic properties of pristine and SBA-15 grafted CuNi bimetallic systems are studied by p-nitrophenol reduction. © 2014 Elsevier Inc. All rights reserved.